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Description  |
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TECHNICAL FIELD
The present invention relates to an electrode substrate for a liquid
crystal display device and to a liquid crystal display device.
BACKGROUND ART
The use of transparent plastic materials as substrates for liquid crystal
display devices instead of glass substrates is being studied. For example,
the liquid crystal display device indicated in Japanese Unexamined Patent
Publication No. 59-204545 has an electrode substrate comprising a 0.1-0.4
mm-thick thermoplastic resin [for example, PES (polyethersulfone), PMMA
(polyethyl methacrylate), PC (polycarbonate) or PET (polyethylene
terephthalate)]substrate, a 15 nm-thick SiO.sub.x undercoat film, a 20
nm-thick ITO transparent conductive film and an orientated directional
film.
When the above-mentioned electrode substrate is introduced into the
production process for an already existing liquid crystal display device
in the same manner as a conventional glass substrate, the following
problems occur.
1. In the alkali treatment and heat treatment processes following
photoetching, cracks result in the SiO.sub.x undercoat film and ITO film,
making further working impossible. Even if it is possible to fabricate a
display device without such cracks, in reliability testing
(high-temperature high-humidity preservation test, cooling/heating thermal
shock test, etc.) cracks in the ITO film make, the ITO electrode broken,
and cracks in the SiO.sub.x film generate air bubbles in the liquid
crystal layer of the display section.
2. Since a thermoplastic resin is used, the rigidity (or "hardness") is
insufficient even with a substrate with a thickness of 0.4 mm, and thus
single-substrate-processing is difficult to perform in the same manner as
for glass substrates. Furthermore, since the softening point of the
substrate is about 100.degree. C., deformation occurs during the heating
and pasting processes, and it becomes impossible to obtain uniform cell
gaps, thus resulting in display irregularities.
3. In cases where the gas barrier properties of the SiO.sub.x undercoat are
unsatisfactory, gases such as O.sub.2 and H.sub.2 O permeate the liquid
crystal layer, resulting in the creation of air bubbles.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a liquid crystal
display device electrode substrate with excellent heat resistance,
abrasion resistance, flatness and gas barrier properties, as well as a
liquid crystal display device employing it.
The electrode substrate for liquid crystal display devices according to the
present invention comprises the following layers A, B, C and E, laminated
in that order.
Layer A: A resin substrate comprising a transparent resin of a copolymer
containing not less than 20% by weight of maleimide type monomer units,
having a crosslinked structure and having a glass transition temperature
of not lower than 160.degree. C. and not higher than 200.degree. C., and
with a thickness of 0.1 to 0.8 mm.
Layer B: A cured coating comprising a polyvinyl alcohol crosslinked with an
epoxysilane represented by the general formula (1) and/or a hydrolysate
thereof:
R.sup.1 SiX.sub.3 ( 1)
wherein R.sup.1 is an organic group of 1 to 10 carbon atoms having a
glycidyl group and X is a hydrolyzable group.
Layer C: A siloxane type cured coating containing fine silica particles.
Layer E: An ITO film having a grainy surface with grains of a diameter of
not larger than 500 nm, formed at a substrate temperature of not higher
than 100.degree. C., and having a thickness of 15 to 500 nm.
This electrode substrate may also have the following layer D between the
aforementioned layers C and E.
Layer D: A metal oxide film comprising a metal selected from Si, Al and Ti,
formed at a substrate temperature of not higher than 100.degree. C. and
having a thickness of 10 to 200 nm.
The liquid crystal display device according to the present invention is
provided with a pair of such electrode substrates which are oriented and
with a liquid crystal layer created by injecting liquid crystals between
the electrode substrates.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical cross-sectional illustration showing an embodiment of
a liquid crystal display device according to the present invention.
FIG. 2 is a vertical cross-sectional illustration showing another
embodiment of a liquid crystal display device according to the present
invention.
FIG. 3 is a photograph of the surface particle structure of the ITO film
obtained in Example 1.
BEST MODE FOR CARRYING OUT THE INVENTION
A concrete explanation of the present invention is provided below.
A. Resin substrate
The transparent resin of the present invention has a glass transition
temperature of not lower than 160.degree. C. and not higher than
200.degree. C. The glass transition temperature is the temperature at
which a macromolecule converts from an amorphous glassy state to a rubber
state. Since the various properties including the elastic modulus,
expansion coefficient, heat content, refractive index and dielectric
constant change within the transition range, it is possible to measure the
glass transition temperature by the changes in these properties.
Specifically, the measurement may be made by a publicly known method such
as differential scanning calorimetry (DSC) (for example, JIS K7121).
In cases where the glass transition temperature of the transparent resin is
less than 160.degree. C., this will result in insufficient heat resistance
during the working processes required for the liquid crystal display
device electrode substrate (in particular, insufficient heat resistance
during the alignment film curing process and the substrate pasting
process), thus making it impossible to perform working for production of
the liquid crystal display device. On the other hand, resins with a glass
transition temperature exceeding 200.degree. C. have insufficient
toughness, leading to cracks in the substrate which complicate its use.
The mechanical properties of the transparent resin, when expressed in terms
of the flexural modulus at room temperature, are preferably 200
kg/mm.sup.2 or greater, and more preferably 330 kg/mm.sup.2 or greater.
Furthermore, the transparency of the transparent resin, when expressed in
terms of the total light transmittance of the resin without coloring, is
preferably 60% or greater, and more preferably 80% or greater.
The transparent resin may also be constructed as a composite system with an
inorganic material or the like, provided that its transparency is not
impaired, and it may include inorganic bonds such as siloxane bonds or
phosphazene bonds.
As transparent resins with glass transition temperatures of not lower than
160.degree. C. and not higher than 200.degree. C., there may be mentioned
(i) polyolefin resins represented by polymethacrylic resins such as
polymethacrylic acid and polycarboxyphenyl methacrylamide and polystyrene
resins such as poly(biphenyl)styrene; (ii) polyether resins represented by
poly(2,6-dimethyl-1,4-phenylene oxide); (iii) polycarbonate resins
represented by poly(oxycarbonyloxy-1,4-phenyleneisopropylidene
-1,4-phenylene); (iv) polyester resins represented by
poly(oxy-2,2,4,4-tetramethyl-1,3-cyclobutyleneoxyterephthaloyl); (v)
polysulfone resins represented by
poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) and
poly(oxy-1,4-phenyleneisopropylidene-1,4-phenyleneoxy
-1,4-phenylenesulfonyl-1,4-phenylene); (vi) polyamide resins represented
by poly(iminoisophthaloylimino-4,4'-biphenylene); (vii) polysulfide resins
represented by poly(thio-1,4-phenylenesulfonyl -1,4-phenylene); (viii)
unsaturated polyester resins; (ix) epoxy resins; (x) melamine resins; (xi)
phenol resins; (xii) diallyl phthalate resins; (xiii) polyimide resins;
and (xiv) polyphosphazene resins. Crosslinked structures may be introduced
into these high molecular groups to obtain transparent crosslinked resins
exhibiting the aforementioned thermal properties.
Polyolefin resins are particularly preferred from the viewpoint of
transparency and moldability, and preferred for use are polyolefin
copolymers obtained by copolymerizing a composition containing
multifunctional monomer units with 2 or more unsaturated groups. The
above-mentioned copolymer is preferably a copolymer containing 20 to 98%
by weight of maleimide monomer units represented by the general formula
(2) below and 2 to 80% by weight of multifunctional monomer units with 2
or more unsaturated groups, and is prepared by polymerizing a composition
with a total weight percentage of not less than 30% by weight of the
above-mentioned monomer units represented by the general formula (2) and
the abovementioned multifunctional monomer units with 2 or more
unsaturated groups.
##STR1##
In the above formula, R.sup.2 and R.sup.3 each independently represent
hydrogen, methyl or ethyl, and R.sup.4 represents hydrogen or a
hydrocarbon group of 1 to 20 carbon atoms. Specific examples of R.sup.4 as
a hydrocarbon group include (i) linear alkyl groups such as methyl, ethyl,
propyl, octyl and octadecyl; (ii) branched alkyl groups such as isopropyl,
sec-butyl, tert-butyl and isopentyl; (iii) alicyclic hydrocarbon groups
such as cyclohexyl and methylcyclohexyl; (iv) aryl groups such as phenyl
and methylphenyl; and (v) aralkyl groups such as benzyl and phenethyl.
Also, the methyl and ethyl group of R.sup.2 and R.sub.3 and the
hydrocarbon group of R.sup.4 may be substituted with any of a variety of
substituents including halogens such as fluorine, chlorine and bromine,
cyano groups, carboxyl groups, sulfonate groups, nitro groups, hydroxy
groups, alkoxy groups, etc.
Specific examples of compounds represented by general formula (2) include
N-methylmaleimide, N-butylmaleimide, N-phenylmaleimide,
N-o-methylphenylmaleimide, N-m-methylphenylmaleimide,
N-p-methylphenylmaleimide, N-o-hydroxyphenylmaleimide,
N-m-hydroxyphenylmaleimide, N-p-hydroxyphenylmaleimide,
N-methoxyphenylmaleimide, N-m-methoxyphenylmaleimide,
N-p-methoxyphenylmaleimide, N-o-chlorophenylmaleimide,
N-m-chlorophenylmaleimide, N-p-chlorophenylmaleimide,
N-o-carboxyphenylmaleimide, N-p-carboxyphenylmaleimide,
N-p-nitrophenylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide and
N-isopropylmaleimide. These monomer units may be used alone or in mixtures
of 2 or more.
From the point of view of yellowing after heat resistance testing and
weatherability, of the above maleimide compounds there are particularly
preferred alkylmaleimides and cycloalkylmaleimides, and
N-isopropylmaleimide and N-cyclohexylmaleimide are even more preferred.
From the point of view of ease of preparation of the monomer solution for
cast polymerization, the combined use of an N-alkylmaleimide and
N-alicyclicalkylmaleimide, for example the combined use of
N-isopropylmaleimide and N-cyclohexylmaleimide, is most preferred. The
proportion of the N-alkylmaleimide and N-alicyclicalkylmaleimide when
these are used in combination should be determined by appropriate
experimentation, depending on the type and amounts of the multifunctional
monomer units with 2 or more unsaturated groups. In order to bring out the
effect of the combined use, the N-alicyclicmaleimide is preferably used at
from 10 to 500 parts by weight to 100 parts by weight of the
N-alkylmaleimide.
The multifunctional monomer units with 2 or more unsaturated groups are
monomers with 2 or more unsaturated functional groups which are
copolymerizable with the above-mentioned maleimide, and the
copolymerizable functional groups may be vinyl, methylvinyl, acryl,
methacryl or the like. They may also be monomers with 2 or more different
copolymerizable functional groups per molecule.
B. Cured coating containing polyvinyl alcohol
The polyvinyl alcohol in the cured coating which is useful according to the
present invention is preferably one with an average polymerization degree
of 250 to 3000. If the average polymerization degree is less than 250, the
resulting film will lack durability (particularly water resistance). Also,
if it exceeds 3000, the viscosity will be too high after coating, thus
leading to working problems such as inability to obtain a smooth coat.
The use of an epoxysilane and a curing agent in the cured coating is
preferred from the standpoint of improving durability, adhesion with the
transparent resin substrate, water resistance and the hydrochloric acid
resistance necessary for etching after setting a conductive film. In
addition, one or more types of epoxysilanes and curing agents may be
added.
A compound represented by the general formula (1) above or a hydrolysate
thereof is suitable as the epoxysilane.
Specific examples of such a compound include glycidoxy
methyltrimethoxysilane, glycidoxy methyltriethoxysilane, .alpha.-glycidoxy
ethyltrimethoxysilane, .alpha.-glycidoxy ethyltriethoxysilane,
.beta.-glycidoxy ethyltrimethoxysilane, .beta.-glycidoxy
ethyltriethoxysilane, .alpha.-glycidoxy propyltrimethoxysilane,
.alpha.-glycidoxy propyltriethoxysilane, .beta.-glycidoxy
propyltrimethoxysilane, .beta.-glycidoxy propyltriethoxysilane,
.gamma.-glycidoxy propyltrimethoxysilane, .gamma.-glycidoxy
propyltriethoxysilane, .gamma.-glycidoxy propyltripropoxysilane,
.gamma.-glycidoxy propyltributoxysilane, .gamma.-glycidoxy
propyltriphenoxysilane, .alpha.-glycidoxy butyltrimethoxysilane,
.alpha.-glycidoxy butyltriethoxysilane, .beta.-glycidoxy
butyltrimethoxysilane, .beta.-glycidoxy butyltriethoxysilane,
.gamma.-glycidoxy butyltrimethoxysilane, .gamma.-glycidoxy
butyltriethoxysilane, .delta.-glycidoxy butyltrimethoxysilane,
.delta.-glycidoxy butyltriethoxysilane, (3,4-epoxycyclohexyl)
methyltrimethoxysilane, (3,4-epoxycyclohexyl) methyltriethoxysilane,
.beta.-(3,4-epoxycyclohexyl) ethyltrimethoxysilane,
.beta.-(3,4-epoxycyclohexyl) ethyltriethoxysilane,
.beta.-(3,4-epoxycyclohexyl) ethyltripropoxysilane,
.beta.-(3,4-epoxycyclohexyl) ethyltributoxysilane,
.beta.-(3,4-epoxycyclohexyl) ethyltriphenoxysilane,
.gamma.-(3,4-epoxycyclohexyl) propyltrimethoxysilane,
.gamma.-3,4-epoxycyclohexyl) propyltriethoxysilane,
.delta.-(3,4-epoxycyclohexyl) butyltrimethoxysilane,
.delta.-(3,4-epoxycyclohexyl) butyltriethoxysilane, and hydrolysates
thereof. The cured coating containing the polyvinyl alcohol crosslinked
with an epoxysilane may contain one or more of these epoxysilanes.
These epoxysilanes are preferably hydrolyzed for use in order to lower the
curing temperature and further promote curing. The hydrolysate may be
obtained by adding pure water or an acidic aqueous solution of
hydrochloric acid, acetic acid, sulfuric acid or the like and stirring.
The degree of hydrolyzation may be easily controlled by adjusting the
amount of the pure water or acidic aqueous solution added. During the
hydrolyzation, addition of pure water or acidic aqueous solution at from 1
to 3 molar equivalents with respect to the hydrolyzable group contained in
the compound represented by general formula (1) is preferred from the
point of view of promoting curing.
Alternatively, in order to produce alcohol, etc., during the hydrolyzation,
the reaction may be carried out without a solvent. Also, for uniform
hydrolyzation, it may be carried out after mixing the epoxysilane and the
solvent. Depending on the purpose, an appropriate amount of the alcohol,
etc., produced by the hydrolyzation may be removed by heating and/or under
reduced pressure and used, and an appropriate solvent added thereafter.
A curing catalyst is preferably added to promote the curing reaction of the
coating. Aluminum chelate compounds are suitable for use as curing
catalysts. Examples thereof are aluminum chelate compounds represented by
the general formula A1X.sub.n Y.sub.3-n. In this formula, X is OL (where L
represents a lower alkyl group of 1 to 6 carbon atoms), Y is at least one
selected from ligands derived from compounds represented by M.sup.1
COCH.sub.2 COM.sup.2 (where M.sup.1 and M.sup.2 both represent lower alkyl
groups) and ligands derived from compounds represented by the general
formula M.sup.3 COCH.sub.2 COOM.sup.4 (where M.sup.3 and M.sup.4 are both
lower alkyl groups of 1 to 6 carbon atoms), and n is 0, 1 or 2.
A number of different compounds may be mentioned as aluminum chelate
compounds represented by this general formula, but from the point of view
of stability and solubility in the composition and effect as curing
catalysts, aluminum acetylacetonate, aluminum bisethylacetoacetate
monoacetylacetonate, aluminum-di-n-butoxido -monoethylacetoacetate,
aluminum-di-iso-propoxido -monomethylacetoacetate, etc., are particularly
preferred. These aluminum chelate compounds may be used alone or in
mixtures of 2 or more.
According to the present invention, for the purpose of improving the
hardness, fine inorganic particles may also be added to the cured coating
containing the polyvinyl alcohol crosslinked with the epoxysilane. The
fine inorganic particles to be used here are not particularly restricted
provided that the transparency of the substrate is not impaired.
Colloidally dispersed sols are particularly preferred examples from the
point of view of improving workability and maintaining transparency. As
more specific examples there may be mentioned antimony oxide sols, silica
sols, titania sols, zirconia sols, alumina sols and tungsten oxide sols.
In order to improve the dispersability of the fine inorganic particles,
any type of fine particle surface treatment or addition of surfactants or
amines may be employed.
The amount of the fine inorganic particles to be added is not particularly
limited, but for a more notable effect the transparent coating preferably
contains the particles at not less than 1% by weight and not more than 80%
by weight. At an amount of less than 1% by weight no clear effect of the
addition will be realized. An amount greater than 80% by weight will lead
to problems such as poor adhesion with the plastic substrate, cracking in
the coating itself, and lower impact resistance.
The size of the fine inorganic particles is not particularly limited, but
is preferably 1 to 200 nm, and more preferably 5 to 100 nm. In cases where
the average particle size is not at least about 1 nm, the stability of the
dispersion is poor, and the quality is not stable. In cases where the
average particle size exceeds 200 nm, the transparency of the resulting
film is poor, and there is a high degree of clouding.
The means of applying the cured coating on the resin substrate may be a
common means of application such as brush coating, immersion coating, roll
coating, spray coating, flow coating, or the like.
C. Siloxane type cured coating
The siloxane type cured coating is a cured coating containing fine silica
particles and a silicone type macromolecule. Other macromolecules may be
added to the cured coating, and three-dimensional crosslinking may also be
performed using a curing agent or crosslinking agent. In consideration of
the properties such as surface harness, heat resistance, chemical
resistance and transparency, the silicone type macromolecule is preferably
a polymer obtained from either an organic silicon compound represented by
the following general formula (3) or a hydrolysate thereof.
R.sup.5.sub.a R.sup.6.sub.b SiX.sub.4-a-b (3)
wherein R.sup.5 is an organic group of 1 to 10 carbon atoms, R.sup.6 is a
hydrocarbon group or halogenated hydrocarbon group of 1 to 6 carbon atoms,
X is a hydrolyzable group, and a and b are 0 or 1.
Examples of organic silicon compounds represented by general formula (3)
include tetraalkoxysilanes such as methyl silicate, ethyl silicate,
n-propyl silicate, isopropyl silicate, n-butyl silicate, sec-butyl
silicate, t-butyl silicate, and hydrolysates thereof; trialkoxysilanes,
triacyloxysilanes and triphenoxysilanes such as methyltrimethoxysilane,
methyltriethoxysilane, methyltriacetoxysilane, methyltripropoxysilane,
methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane,
vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane,
phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriacetoxysilane,
.gamma.-chloropropyltrimethoxysilane, .gamma.chloropropyltriethoxysilane,
.gamma.-chloropropyltriacetoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
.gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltriethoxysilane,
.gamma.-mercaptopropyltrimethoxysilane,
.gamma.-mercaptopropyltriethoxysilane, N-.beta.-(aminoethyl)-
.gamma.aminopropyltrimethoxysilane, .beta.-cyanoethyltriethoxysilane,
methyltriphenoxysilane, chloromethyltrimethoxysilane,
chloromethyltriethoxysilane, glycidoxy methyltrimethoxysilane, glycidoxy
methyltriethoxysilane, .alpha.glycidoxy ethyltrimethoxysilane,
.alpha.-glycidoxy ethyltriethoxysilane, .beta.-glycidoxy
ethyltrimethoxysilane, .beta.-glycidoxy ethyltriethoxysilane,
.alpha.-glycidoxy propyltrimethoxysilane, .alpha.-glycidoxy
propyltriethoxysilane, .beta.-glycidoxy propyltrimethoxysilane,
.beta.-glycidoxy propyltriethoxysilane, .gamma.-glycidoxy
propyltrimethoxysilane, .gamma.-glycidoxy propyltriethoxysilane,
.gamma.-glycidoxy propyltripropoxysilane, .gamma.-glycidoxy
propyltributoxysilane, .gamma.-glycidoxy propyltriphenoxysilane,
.alpha.-glycidoxy butyltrimethoxysilane, .alpha.-glycidoxy
butyltriethoxysilane, .beta.-glycidoxy butyltrimethoxysilane,
.beta.-glycidoxy butyltriethoxysilane, .gamma.-glycidoxy
butyltrimethoxysilane, .gamma.-glycidoxy butyltriethoxysilane,
.delta.-glycidoxy butyltrimethoxysilane, .delta.-glycidoxy
butyltriethoxysilane, (3,4-epoxycyclohexyl) methyltrimethoxysilane,
(3,4-epoxycyclohexyl) methyltriethoxysilane, .beta.-(3,4-epoxycyclchexyl)
ethyltrimethoxysilane, .beta.-(3,4-epoxycyclohexyl) ethyltriethoxysilane,
.beta.-(3,4-epoxycyclohexyl) ethyltripropoxysilane,
.beta.-(3,4-epoxycyclohexyl) ethyltributoxysilane,
.beta.-(3,4-epoxycyclohexyl) ethyltriphenoxysilane,
.gamma.-(3,4-epoxycyclohexyl) propyltrimethoxysilane,
.gamma.-3,4-epoxycyclohexyl) propyltriethoxysilane,
.delta.-(3,4-epoxycyclohexyl) butyltrimethoxysilane,
.delta.-(3,4-epoxycyclohexyl) butyltriethoxysilane, and hydrolysates
thereof; and dialkoxysilanes, diphenoxysilanes and diacyloxysilanes such
as dimethyldimethoxysilane, phenylmethyldimethoxysilane,
dimethyldiethoxysilane, phenylmethyldiethoxysilane,
.gamma.-chloropropylmethyldimethoxysilane,
.gamma.-chloropropylmethyltriethoxysilane, dimethyldiacetoxysilane,
.gamma.-methacryloxy propylmethyldimethoxysilane, .gamma.-methacryloxy
propylmethyldiethoxysilane, .gamma.-mecaptopropylmethyldimethoxysilane,
.gamma.-mercaptopropylmethyldiethoxysilane,
.gamma.-aminopropylmethyldimethoxysilane,
.gamma.-aminopropylmethyldiethoxysilane, methylvinyldimethoxysilane,
methylvinyldiethoxysilane, glycidoxy methylmethyldimethoxysilane,
glycidoxy methylmethyldiethoxysilane, .alpha.-glycidoxy
ethylmethyldimethoxysilane, .alpha.-glycidoxy ethylmethyldiethoxysilane,
.beta.-glycidoxy ethylmethyldimethoxysilane, .beta.-glycidoxy
ethylmethyldiethoxysilane, .alpha.-glycidoxy propylmethyldimethoxysilane,
.alpha.-glycidoxy propylmethyldiethoxysilane, .beta.-glycidoxy
propylmethyldimethoxysilane, .beta.-glycidoxy propylmethyldiethoxysilane,
.gamma.-glycidoxy propylmethyldimethoxysilane, .gamma.-glycidoxy
propylmethyldiethoxysilane, .gamma.-glycidoxy propylmethyldipropoxysilane,
.gamma.-glycidoxy propylmethyldibutoxysilane, .gamma.-glycidoxy
propylmethylmethoxyethoxysilane, .gamma.-glycidoxy
propylmethyldiphenoxysilane, .gamma.-glycidoxy
propylmethyldiacetoxysilane, .gamma.-glycidoxy propylethyldimethoxysilane,
.gamma.-glycidoxy propylethydiethoxysilane, .gamma.-glycidoxy
propylvinyldimethoxysilane, .gamma.-glycidoxy propylvinyldiethoxysilane,
.gamma.-glycidoxy propylphenyldimethoxysilane,
.gamma.-propylphenyldiethoxysilane, and hydrolysates thereof.
Any one or more of these organic silicon compounds may be added.
To the coating-forming composition consisting mainly of the silicone resin
there may also be added, in addition to the silicon resin, an acrylic
resin, polyurethane resin, epoxy resin, melamine resin, polyolefin resin,
cellulose, polyvinyl alcohol resin, urea resin, nylon resin, polycarbonate
resin, or the like. The additional resins are not particularly limited
provided that they do not impair the transparency and that sufficient
surface hardness is achieved.
These organic silicon compounds are preferably hydrolyzed for use in order
to lower the curing temperature and further promote curing. The
hydrolyzation may be carried out by adding pure water or an acidic aqueous
solution of hydrochloric acid, acetic acid, sulfuric acid or the like and
stirring. The degree of hydrolyzation may be easily controlled by
adjusting the amount of the pure water or acidic aqueous solution added.
During the hydrolyzation, addition of pure water or acidic aqueous
solution at from 1 to 3 molar equivalents with respect to the hydrolyzable
group contained in the compound represented by the above general formula
(3) is preferred from the point of view of promoting curing.
Alternatively, in order to produce alcohol, etc., during the hydrolyzation,
the reaction may be carried out without a solvent. Also, for uniform
hydrolyzation, it may be carried out after mixing the organic silicon
compound and the solvent. Depending on the purpose, an appropriate amount
of the alcohol, etc., produced by the hydrolyzation may be removed by
heating and/or under reduced pressure and used, and an appropriate solvent
added thereafter.
Fine silica particles may also be added to the siloxane type cured coating
for the purpose of improving the surface hardness, adjusting the
refractive index, improving the mechanical strength, improving the thermal
properties, etc. Fine silica particles are useful with no particular
restrictions provided that the transparency is not impaired when in a film
state. Colloidally dispersed sols are particularly preferred examples from
the point of view of improving workability and imparting transparency. In
order to improve the dispersability of the fine silica particles, any type
of fine particle surface treatment or addition of surfactants or amines
may be employed.
The amount of the fine silica particles to be added is not particularly
limited, but for a more notable effect the transparent coating preferably
contains the particles at not less than 1% by weight and not more than 80%
by weight. At an amount of less than 1% by weight no clear effect of the
addition will be realized. On the other hand, an amount greater than 80%
by weight will lead to problems such as poor adhesion with the plastic
substrate, cracking in the coating itself, and lower impact resistance.
The size of the fine silica particles is not particularly limited, but is
preferably 1 to 200 nm, and more preferably 5 to 100 nm. In cases where
the average particle size is not at least about 1 nm, the stability of the
dispersion is poor, and the quality is not stable. In cases where the
average particle size exceeds 200 nm, the transparency of the resulting
film is poor, and there is a high degree of clouding.
Any of a variety of curing agents may be used in combination with the
coating composition for forming the siloxane type cured coating, in order
to promote curing and allow low temperature curing, etc. Useful curing
agents include various epoxy resin curing agents and organic silicon resin
curing agents. Specific examples of curing agents are (1) various organic
acids and their acid anhydrides, (2) nitrogen-containing organic
compounds, (3) various metal complex compounds (4) metal alkoxides, (5)
organic carboxylic acid salts and carbonic acid salts and peroxides of
alkali metals, and (6) radical polymerization initiators such as
azobisisobutyronitrile. These curing agents may also be used in
combinations of 2 or more. Of these curing agents, the aluminum chelate
compounds indicated below are particularly useful from the point of view
of stability of the coating composition and coloring of the film after
coating.
For example, preferred for use are aluminum chelate compounds represented
by the general formula A1X.sub.n Y.sub.3-n. In this formula, X is OL
(where L represents a lower alkyl group of 1 to 6 carbon atoms), Y is at
least one selected from ligands derived from compounds represented by
M.sup.1 COCH.sub.2 COM.sup.2 (where M.sup.1 and M.sup.2 both represent
lower alkyl groups of 1 to 6 carbon atoms) and ligands derived from
compounds represented by the general formula M.sup.3 COCH.sub.2 COOM.sup.4
(where M.sup.3 and M.sup.4 are both lower alkyl groups of 1 to 6 carbon
atoms), and n is 0, 1 or 2.
A number of different compounds may be mentioned as aluminum chelate
compounds represented by this general formula, but from the point of view
of solubility and stability in the composition and effect as curing
catalysts, aluminum acetylacetonate, aluminum bisethylacetoacetate
monoacetylacetonate, aluminum-di-n-butyoxido-monoethylacetoacetate,
aluminum-di-iso-propoxido-monomethylacetoacetate, etc., are particularly
preferred. These aluminum chelate compounds may be used alone or in
mixtures of 2 or more.
The siloxane type cured coating may be obtained by curing the
above-mentioned coating composition, and the curing is accomplished by
heat treatment. The heating temperature may be appropriately selected with
consideration to the composition of the coating composition and the heat
resistance of the transparent crosslinked resin, and it is preferably
50.degree.-250.degree. C.
The means of applying the coating on the coating resin substrate may be a
common means of application such as brush coating, immersion coating, roll
coating, spray coating, spin coating, flow coating, or the like.
D. Metal oxide film
The metal oxide film formed on the substrate with the cured coating
preferably comprises an oxide of a metal selected from Si, Al and Ti. The
thickness of the metal oxide film is preferably 10 to 200 nm, and more
preferably 10 to 120 nm, from the point of view of masking the substrate
surface and providing adhesion with the ITO film.
In addition, from the point of view of minimizing deformity in the
substrate at normal temperature after formation of the metal oxide film,
due to differences between the thermal expansion coefficient of the metal
oxide film and the thermal expansion coefficient of the substrate with the
cured coating, the substrate temperature conditions during formation of
the metal oxide film are preferably at low temperatures of as close to
normal temperature as possible, and preferably 100.degree. C. or lower.
E. ITO film
The method of forming the ITO (Indium Tin Oxide) film on the substrate with
the metal oxide film may be vacuum deposition, ion plating, direct
current, magnetron system sputtering, or the like.
The thickness of the ITO film is not particularly limited, but is
preferably within the range of 15 to 500 nm in consideration of the
relationship between the resistance value and the film formation time.
The surface structure of the ITO film is preferably grainy in consideration
of the durability of the ITO film. Graininess refers to a structure in
which morphological observation with an electron microscope or atomic
force microscope reveals a grain boundary in the ITO film surface such as
shown in FIG. 3. The grains preferably have a diameter of not more than
500 nm.
The substrate temperature conditions during formation of the ITO film are
preferably not higher than 100.degree. C., from the point of view of
minimizing deformity in the substrate at normal temperature after
formation of the ITO film (substrate deformities which create raised areas
in the ITO surface) due to differences in the thermal expansion
coefficients of the substrate and the ITO film.
F. Liquid crystal display device
The electrode substrate for liquid crystal display devices is obtained by
forming the above-mentioned cured coating containing a polyvinyl alcohol
for improved gas barrier properties, the above-mentioned siloxane type
cured coating containing fine silica particles for an improved hard coat
effect, and the above-mentioned metal oxide film and ITO film for improved
adhesion under temperature conditions of not more than 100.degree. C. in
order to minimize substrate deformities, in that order on the
above-mentioned resin substrate comprising a transparent resin with a
crosslinked structure. This type of substrate provides transparency, heat
resistance, gas barrier properties, abrasion resistance and substrate
deformity control.
Nevertheless, in cases where the results of reliability evaluation are
satisfactory, the metal oxide film may be omitted from the structure.
In cases where the above-mentioned electrode substrate is to be given a
transparent conductive film, its thickness is preferably 0.1 to 5 mm, in
consideration of the mechanical characteristics. Also, in cases where it
is to be used for a liquid crystal display, it is more preferably 0.1 to
0.8 mm thick. This is because at less than 0.1 mn the form retention is
inadequate, and at greater than 0.8 mm the thinness and lightweight
effects are reduced.
This electrode substrate for liquid crystal display devices is suitable to
be used for liquid crystal displays of the (i) simple matrix type such as
TN (Twisted Nematic) type, STN (Super Twisted Nematic) type and FLC
(Ferroelectric Liquid Crystal) type, (ii) PD (Polymer Dispersion) type,
and (iii) active matrix type such as MIM (Metal-Insulator-Metal) type and
TFT (Thin-Film Transistor) type, etc. Since the production process for the
electrode substrate is relatively simple, it is preferably used for simple
matrix type liquid crystal displays.
A publicly known method may be employed for producing a liquid crystal
display device using the electrode substrate for liquid crystal display
devices according to the present invention. For example, in the case of
simple matrix liquid crystal displays [see Liquid Crystal Device Handbook
(Japan Society for the Promotion of Science, 142nd Committee Edition,
published by Nikkan Kogyo Shinbun Co., 1989), p.531], liquid crystal
display devices are obtained by a process including a substrate washing
step, a transparent conductive film forming step, a transparent conductive
film patterning (resist application, development, etching and resist
washing and removal) step, an alignment film forming step, a rubbing
treatment step, a washing step, a sealant printing step, a substrate
pasting step, a heating/pressing step, a vacuum deairing step, a liquid
crystal injection step, an injection hole sealing step, a liquid crystal
cell segmenting step, and a polarization plate/reflection plate pasting
step, in that order. In these steps for producing a liquid crystal display
device, the conditions should be set in consideration of the various
properties of the electrode substrate for the liquid crystal display
device, such as heat resistance and mechanical characteristics.
A particularly preferred method of producing a liquid crystal display
device is given below.
An electrode substrate according to the present invention is washed and
coated with a photoresist to a thickness of 1-3 .mu.m by a roll coat
system, and then prebaked for a few minutes at 80.degree.-130.degree. C.
After this, it is exposed to light using a desired photomask. The
developing solution used is a 0.6% wt % aqueous NaOH solution (25.degree.
C.). The amount of exposure and developing time, etc., are set for optimum
conditions based on the sensitivity of the photoresist, the prebaking
conditions, and so on.
After development, the ITO film is etched with a 3-8.6 N aqueous HBr
solution (30.degree.-45.degree. C.) and the photoresist is washed and
removed using a 3 wt % aqueous NaOH solution (30.degree. C.), to obtain a
transparent conductive film electrode substrate.
On the substrate on which is formed the transparent conductive film
electrode pattern, there is printed a silica coating material to a
thickness of 50-150 nm by offset printing, and firing is performed at
150.degree.-170.degree. C. with a peak at 60 minutes to form a top coat.
This top coat prevents leakage due to conductive impurities between the
ITO film and the pasted upper and lower substrates.
At the same time as the top coat formation, an alignment film material,
such as polyimide, is printed over the top coat film by offset printing to
a film thickness of 30-60 nm, and firing is performed at
150.degree.-170.degree. C. with a peak at 90 minutes to form an alignment
film. In addition, the alignmen | | |
